A sheet pile's main function is to withstand sideways loading. Sheet piles are thus used to form retaining walls in various applications, including basement excavations, underground car parks, and cofferdams. Sheet piles may also be used in forming level roadways on embankments or for stabilising slope failures.
An advantage of sheet piles is that, owing to their relatively small cross sectional area, they may be driven into the ground either by means of a drop hammer or a vibratory hammer. Sheet piles, if adequate for a particular application, are often preferable to alternative forms of retaining wall which include contiguous bore piles, soldier bore piles with lagging and diaphragm walls. Use of sheet piles eliminates time consuming and costly site preparation work associated with the use of such alternatives and significantly reduces material costs.
Numerous difficulties may be encountered during manufacture and/or assembly of many existing types of sheet piling.
One such difficulty may arise during driving. Sheet piles are driven into the earth one by one, the sheet pile being driven being interconnected with an adjacent sheet pile driven before it. The end of the pile being driven may encounter changes in earth hardness or inclusions such as rocks and pebbles, which can cause it to deflect, thereby subjecting the connection it forms with the adjacent sheet pile to complex loading. Such loading may be in directions the connection is not equipped to cope with. This problem in particular may be encountered where the sheet piles have been cold rolled because such sheet piles can be provided only with relatively simple shaped connectors able to permit substantially unidirectional loading. Loading of the connectors of sheet piles in a direction with which they are not equipped to cope, particularly during driving, can cause the connections to jam. Where the loading is sufficiently high, the connectors may fail, by unhooking and/or deformation, thus causing the sheet piles to become disconnected.
The stiffness of a sheet pile assembly is largely related to its cross sectional depth in the direction of loading. For heavy duty applications, an assembly of sheet piles must be sufficiently deep in cross section to have the requisite stiffness to withstand the high sideways loads. Where sheet piles in the assembly are identical, this requires either that they individually have sufficient cross sectional depth or that they be able to be arranged at various angles with respect to each other in an assembly whilst still being able to transfer shear between each other in service. Conventional cold rolled sheet piles, as a result of the directional loading constraints on their connectors, must therefore be provided with differing cross sectional configurations. The need for more than one type of cold rolled sheet pile thus creates manufacturing complexity. Also, the abovementioned risks of jamming and disconnection during driving remain.
Some tolerance to misalignment during driving can be achieved by separate hot rolling manufacture of more elaborate connections which also are able to cope at least with a degree of the associated complex loading discussed above.
WO 00/08263 (Horan et al.) discloses a metal sheet pile which comprises a cold formed wall section of sheet material to the longitudinally extending side edges of which are secured hot formed clutch sections. The hot formed clutch sections may be produced by hot rolling or extrusion and must be secured to the cold formed wall sections by welding, bolting, riveting or other means. The requirement that these clutch sections be separately hot rolled represents a significant drawback because of the very high production costs associated with hot rolling. Hot rolling requires complex and extremely expensive plants and infrastructure. It is therefore not economical to produce hot rolled items in small volumes.
Furthermore, the need to manufacture the clutches separately and then fix them to the sheet pile side walls introduces manufacturing complexity and further expense.
The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia or elsewhere as at the priority date of the application.